The invention relates to a method and an arrangement for capacitive seat-occupancy recognition for vehicle seats.
In connection with pertinent vehicle components, such methods and arrangements serve to recognize the occupancy of a vehicle seat by a person, and moreover to undertake classification regarding what type of seat occupancy exists. It must be possible to distinguish whether an object, for example a shopping handbasket, a purse, or similar is located on the seat, whether a child seat (empty or occupied by a child) is located on the seat, or whether an adult is seated.
It is additionally advantageous if the method employed can provide information regarding the seating position of the passenger along with personal classification. Such information would provide data regarding whether the passenger has sat on the seat and has established contact between his/her upper body with the seat back, or whether the passenger has bent far forward and contact with the seat back is not resulting, or no longer exists.
Known systems for seat-occupancy recognition as a rule comprise a sensor system that acquires data at one or at several locations of the seat, plus an electronic evaluation circuit that calculates or derives a classification of the seat occupancy.
Various types of sensors may be used for the acquisition system such as resistive, capacitive, or inductive sensors that alter an electrical measurement signal depending on seat occupancy. These alterations are evaluated by an electronic evaluation circuit, and are assigned to various seat-occupancy statuses. Only resistive and dielectric systems enjoy wide use.
While resistive systems are generally preferred when low expenditures and low costs are important, dielectric systems are preferred when positive recognition of persons and distinction between persons and objects of similar weight and/or similar surface pressure on the seat base, are required.
Such dielectric systems as a rule consist of a defined arrangement of one or several electrodes and a device to apply a defined alternating voltage or pulsed voltage to this arrangement and also be able to acquire the current taken by the system and evaluate it, and from this evaluation to be capable of making a decision regarding the seat occupancy.
These arrangements require on the one hand very specialized circuitry techniques in order both to define the voltage exactly and to measure the current as precisely as possible so that the relatively small dielectric alterations caused by a passenger in the sensor arrangement may be appropriately detected. On the other hand, there is also the requirement with such dielectric systems that the sensors react to water on the seat base or in the sensor arrangement similarly as to the presence of a person, which increases the expense of detection and evaluation significantly if a positive distinction must be made between a signal alteration caused by person or water.
DE 10 2009 050 437 A1 describes a device to detect a close object that is used, for example, to determine the occupancy of a vehicle seat in order to require the person to fasten the seat belt. The device comprises an electrode arrangement that includes at least two stationary electrodes permanently affixed opposite to each other, a source of alternating current to supply the electrode arrangement, and a measurement and evaluation unit to measure the current flowing because of the capacitance caused by the electrodes. The electrodes possess electrode surfaces facing toward the object to be detected, and are at a mutual separation such that the approach of an object into the immediate area of influence of the electrode arrangement leads to a reduction of the measured current that is detected and reported by the measurement and evaluation unit within the parameters defining the presence of an object.
US 2008/0208414 A1 (corresponds to priority document DE 10 2004 047 906 A1) describes a control device to trigger a vehicle passenger-protective device such as an airbag or belt tensioner. This control device comprises a force sensor in the form of a capacitive sensor to receive a force moment acting on the vehicle seat, and a control and evaluation circuit that produces a classification in particular one regarding weight from the sensor signals, and independent of this initiates the safety device for the occupant. The measurement capacitor of the capacitive sensor is deformable by the inertial forces acting on the vehicle so that it changes its capacitance. This revised capacitance is evaluated, and a triggering signal for the safety device is derived.
DE 196 30 769 A1 describes a device and a method to determine the entry of a person into a vehicle and/or the position(s) of person(s) within a vehicle. Two metallic, conducting surfaces or wires electrically isolated from each other that are shaped as the electrodes of one or several plate capacitors are used. These plate capacitors are positioned within the vehicle such that a person entering the vehicle completely or partially passes between these plates. The plate capacitors are frequency-determining elements of a first narrow-band electronic circuit.